Metal plating process



United States Patent i 3,018,194 METAL PLATING PROCESS Vello Norman and Thomas P. Whaley, Baton Rouge, La., assignors to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 3, 1959, Ser. No. 831,077 6 Claims. (Cl. 117-107) This invention relates to the plating of appropriate substrates using polymetallic organometallic compounds. More particularly this invention relates to the plating of alloys on appropriate substrates by the decomposition of bimetallic organometallic compounds.

Heretofore, in order to deposit alloys by the decomposition of organometallic compounds, it has been necessary to employ two difierent mono metal containing compounds. For example, molybdenum-tungsten alloys have been prepared by pyrolysis of the mixed carbonyl vapors, i.e. a mixture of molybdenum carbonyl and tungsten carbonyl. Furthermore, alloys have been produced by hydrogen reduction of the mixed chloride vapors. Thus titanium-tantalum alloys have been obtained by co-deposition from the respective bromides utilizing hydrogen reduction. However, in attempting alloy plating from two different chemical compounds it often happens that a marked difierence exists in the chemical afiinities of the two alloying constituents. In such cases deposition of only one constituent will usually occur to the entire exclusion of the other constituent. Thus, it becomes necessary to, as nearly as possible, equalize rates of deposition by proper choice of deposition temperature. In other words, it becomes necessary to choose chemically compatible compounds as plating agents. Because of this, the choice of available compounds for producing alloy plates from two diiferent mono metal containing compounds becomes considerably narrowed. Consequently the types of feasible alloys also are decreased. According to the present invention, these inherent disadvantages in the prior art processes for plating alloys by decomposition or reduction of difierent metal compounds are overcome by employing bimetallic organometallic compounds in the plating process. By virtue of this plating process vastly improved alloy plates are provided on a wide range of substrates.

Thus, among the objects of this invention is that of providing a process for plating alloys on substrates using bimetallic organometallic compounds. Another object is to provide a decomposition process for plating substrates using these bimetallic organometallic compounds. A further object of this invention is to provide a thermal process for plating substrates by thermal decomposition of bimetallic organometallic compounds. Still another object of this invention is to provide novel and highly useful alloy plated articles made according to these processes. Other important objects of this invention will be apparent from the ensuing description.

According to this invention there is provided a process for alloy plating a substrate by the decomposition of a polymetallic organometallic compound in contact with the substrate. In their broadest aspect the bimetallic organometallic compounds of this invention contain at least two difierent metals. Within the scope of this invention is a process for plating a substrate comprising heating the object to be plated to a temperature above the decomposition temperature of a bimetallic organometallic compound and contacting said compound with said heated substrate. Those bimetallic organometallic compounds which contain as the exclusive constituents of the molecule, two different metals and unsubstituted hydrocarbon radicals are especially useful in vapor phase alloy plating operations. In carrying out these vapor phase techniques the substrate to be alloy plated is heated to a temperature above about 200 C. while maintained under an inert atmosphere such as nitrogen, the rare gases (e.g. neon, argon, krypton, xenon) etc.

Bimetallic organometallic compounds used in this invention and comprising one embodiment thereof can be represented by the general formula wherein M is a metal selected from the group consisting of groups I, II, III-B, IV-B, V-B, VI-B, VII-B, VIII of the periodic chart of the elements and tin and aluminum; M is a difierent metal selected from the group consisting of group III-A of the periodic chart of the elements and zinc and cadmium; R is a monovalent anioni.e. group or radical; x is an integer corresponding to the valence of the metal M; y is an integer corresponding to the valence of the metal M. It is especially preferred that the monovalent anion R be a substituent which upon the decomposition of the bimetallic organometallic plating agent forms decomposition by-products which are devoid of free hydrogen. Hydrogen by-product is particularly undesirable in those cases wherein the alloys to be plated and the substrate are susceptible to hydrogen embrittlement.

The process of this invention presents a significant advance over the prior art in that for the first time it is possible to produce alloy plates from bimetallic organometallic compounds in a simple, safe, economical process. A further advantage of this invention is that through the employment of this process, it becomes possible to produce alloy plates having exceptional purity and excellent adherence to the substrate on which the alloy is plated. Furthermore, the process of this invention provides easy control of the proportionate metallic content of the respective metal of the alloy. That is, because of the ready availability of bimetallic organometallic compounds having wide variation in the percent weight ratio of the different metals contained therein, it is, as a result of this invention, now simply a matter of choosing the compound having a metal content tailor made to producing the desired alloy. Thus, it becomes unnecessary to hunt for compounds having suitable mutual chemical aflinity such as compatible decomposition temperatures, decomposition rates, etc., which heretofore has been such a limiting factor in applying organometallic decomposition technology to the production of alloys. Also, the process of this invention provides easy control of the alloy plate thickness. On the one hand, a micro molecular alloy film can be plated on the substrate and in other cases, if so desired, thicker alloy plates can be obtained. A particular advantage of using bimetallic organometallic compounds which upon decomposition yield by-products which are exclusive of free hydrogen and oxidizing materials is that the alloy plates are thereby obtained free of undesirable oxide impurities and are not deteriorated through hydrogen embrittlement.

In general, any prior art technique for metal plating an object by thermal decomposition of the metal containing compound can be employed in the plating process of this invention as long as a bimetallic organometallic compound is employed as the plating agent (i.e. the metallic source of the metal plate). Thus, for example, any technique heretofore known for the thermal decomposition and subsequent plating of group VI-B metals from the hexacarbonyl derivatives of those metals can be so employed. illustrative are those techniques described by Lander and Germer, American Institute of Mining and Met-allurgical Engineers, Tech. Publication No. 2259 (1947)} Usually the technique to be employed comprises heatin glthe object to be plated to a temperature above thef deicomposition temperature of the metal containing compoundand thereafter contacting the metal containing compoundwith the heated object. The following example s are; more fully illustrative of the process of this invention and in these and other working examples all parts and percentages are by weight.

The process employed in these examplesis as follows: Into a conventional heating chamber provided with means forihigh frequency induction heating and gas inlet and outlet means is placed the object to be plated. The bimetallic organometallic compound is placed in a standard vaporization chamber provided with heating means, said vaporization chamber being connected through an outlet port to the aforesaid combustion chamber inlet means.

Forthe plating operation the substrate is heated to a temperature abovethe decomposition temperature of the bimetallic. organometallic plating agent, the system is evacuatedfand the organometallic compound is heated to an appropriate temperature where it possesses vapor pres-. sureof up to about 10 millimeters. In most instances the process is conducted at no lower than 0.01 millimeter pressure, The yapors of the bimetallic organometallic compound are pulled through the system as the evacuating'nieans' operates and they impinge on the heated object decomposing and forming alloy plates. No carrier gas need be employed. However, in certain cases a carrier gas can be employed to' increase the efficiency of the above disclosed plating system. In those cases where 40 a carrier gas is employed, asystern such as described by Lander and Germer, American Institute of Mining and Metallurgical Engineers, Tech. Publication No. 2259 (1947), at page 7, can be utilized.

Example I Compound Sn(AlEt (tin bis (aluminum tetraethyl)). Temp. of.substrate 350 C.

Nature of substrate Pyrex.

Pressure 0.5 mm. Compound temp. 90-100 C. Time, 2 hours. W V Results Dull, grey,'metallic coating.

, Example II Compound Li(AlCp (lithium aluminum tetracyclopentadienide) Temp; of substrate 350 C. Nature of substrate Mild steel." Pressure' 0.1 mm. Compound temp, 150 C. Time lhour. Results' Dull metallic coating.

Example III Compound ".I Li(Al indenide (lithium aluminum tetraindenide). 'f mry tsvb t te- C- 10 Nature of substrate .J; Pyrex; Pressure 0.5 mm. Compoundtemp. 130 C;- Time" 1 hour. Results Dull metallic.

4. Example IV Compound Li(AlEt l-I) (lithium aluminum triethylhydride Temp. of substrate 300 C. Nature of substrate Nickel.

Pressure 3-4 mm. Compound temp. 130 C. Time 1 hour. a Results Dull metallic.

Example V Compound Cp TiCl AlEt: (dicyclopentadie nyltitanium dichloride aluminum diethyl).

Temp. of substrate 250 C.

Nature of substrate Pyrex.

Temp. of substrate 450 C. Nature of substrate Graphite.

Pressure 5 mm.

Compound temp, 75 C.

Time 2% hours; Results Dark grey, dull coating.-

Example VI I Compound Fe(CO) PbEt (iron tetracarbonyl leaddiethyl); Temp. of substrate 400 C. Nature of substrate Mild steel.

Pressure 2 mm.

Compound temp. C.

Time lhour. Results Dark grey, dull coating:

The process employed in Example s 'l and following is utilized with the exception that an ultrasonic generator is proximately positioned to theplating apparatus. The compound is heated to its decomposition threshold'and thereafter the ultrasonic generator is utilized to effect final decomposition;

Example Vl ll num tetraethyl)). Temp. of substrate" 200 C. Nature of substrate Glass wool.

Temp. of substrate 300 C. Nature of substrate Pressure 0.1 mm.

Compound temp, 60 C.

Time 4 hours.

Results Powder, chromium-boride or mix ture.

As discussed hereinbefore the bimetallic d gsnqmttamc plating agents of this invention can be represented by the general formula MtM' xmy wherein M is a metal selected from the group consisting of groups I, II, III-B, IV-B, V-B, VI-B, VII-B, VIII, of the periodic chart of the elements and the metals tin and aluminum; M is a metal selected from the group consisting of group III-A of the periodic chart of the elements and the metals zinc and cadmium; R represents a monovalent anion; x is an integer equal to the valence of M; y is an integer equal to the valence of M.

The metals designated by M include, lithium, sodium, potassium, rubidium, cesium, francium of group I-A. Within this group lithium is the especially preferred metal because of the desirable high temperature characteristics lithium imparts when alloyed with certain metals. The symbol M further designates the metals beryllium, magnesium, calcium, strontium, barium, radium within group II-A; scandium, indium, lanthanum, actinium (including the lanthanum and actinium series) within group III-B; titanium, zirconium, hafnium, within group IV-B; vanadium, niobium, tantalum within group V-B; chromium,

molybdenum, tungsten within group VI-B; manganese, technetium, rhenium within group VII-B; and iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum of group VIII. Within the groups I-B and II-B, M designates the metals silver, copper, gold, zinc, cadmium and mercury. It of course should be recognized that because of the scarcity of certain of the above metals, their use would be reserved for those instances where their unique alloying properties are desired or needed.

The metal M includes any of the elements of group III-A and thus includes boron, aluminum, thallium, indium and gallium. Of these aluminum is most preferred because of its wide availability and use in plating technology.

As noted above, R is a monovalent anion, preferably an unsubstituted hydrocarbon group. The hydrocarbon groups generally contain between about 1 and 20 carbon atoms each. A preferred class of bimetallic organometallic plating agents of this invention contains as one of the R groups at least one cyclopentadienyl group. By a cyclopentadieuyl group is meant groups containing the five carbon atom ring found in cyclopentadiene itself. Examples are the cyclopentadienyl, indenyl'and fluorenyl groups, and the corresponding groups substituted with one or more hydrocarbon radicals such as the methylcyclopentadienyl, methyl-tert-butylcyclopentadienyl, triethylindenyl, phenylcyclopentadienyl and related groups.

R can also be other monovalent anions. These anions include organic hydrocarbon radicals and substituted bydrocarbon radicalsincluding the halogenated hydrocarbon residues of organic acids containing up to about 20 carbon atoms, such as the acetate, propIonate, butyrate, hexanoate. R can also be inorganic anions such as hydrogen, the halides, hydrides; pseudo halides, e.g., cyanates, thiocyanates, cyanides, cyanimides, amides; alcohol residues (OR) wherein the hydrocarbon portions con tain up to about 18 carbon atoms; or inorganic acid anions such as sulfate, nitrate, borate, phosphate, arsenate and the like.

Typical examples of the bimetallic organometallic plating agents of this invention comprise: tin tetramethylboron, chromium tetraethylboron, scandium tetraethylboron, copper tetraisopropylboron, titanium tetraoctylboron, vanadium tetraoctadecylboron, chromium tetraeicosylboron, tin tetravinylboron, iron tetra-Z-butenylboron, cobalt l-hexynyltriethylboron, nickel tetraethynylboron, tin tetracyclohexylboron, vanadium tetraphenylboron, copper tetrabenzylboron, titanium tetranaphthylboron, titanium tetracyclohexenylboron, vanadium tetrabutadienylboron; chromium ethyltributylboron, zirconium ethyltrioctylboron, iron ethyltrioctadecylboron, cobalt ethyltricyclohexylboron, cobalt ethyltriphenylboron, nickel ethyltri(2-phenylethyl)boron, manganese ethyltriisopropylboron, copper diethyldiisopropylboron, titanium diethyldiphenylboron, vanadium diethyldioctadecylboron, chromium octyltrioctadecylboron; molybdenum ethylborontrichloride, trifiuoride, tribromide, or triiodide; iron triethylboron hydride, cobalt trioctylboron hydride; nickel ethyltrimethoxyboron, tungsten triethylethoxyboron, tin trioctylboron octanoate, copper triethylboron cyanide, titanium triphenylboron cyanide, vanadium triethylboron cyanate and thiocyanate; chromium triethylboron amide, molybdenum triethylboron mercaptide, iron triethylboron azide, cobalt triethylboron acetate, nickel triethylboron octanoate, tin triethylboron phenolate; chromium triethylboron sulfate, nitrate, nitrite, sulfite, phosphate, phosphite, arsonate, or chlorate, and the like; also similar compounds wherein other group III-A elements, zinc, or cadmium are substituted for boron as, for example, tin tetraethylaluminum, chromium tetraethylaluminum, zirconium tetraethylaluminum, copper tetraethyl aluminum, tin triethylzinc, titanium triethylzinc, manganese tetraethylaluminum, and the like. It is preferable that the first metal, M, be tin, chromium, copper, vanadium, manganese, iron, cobalt, nickel, or titanium, and the second metal, M, be aluminum or boron with all of the chemical groups attached to the latter being hydrocarbon radicals having up to about 8 carbon atoms, especially the unsubstituted hydrocarbon radical, e.g. alkyl radicals. Compounds of the metals tin, chromium, and copper comprise an especially unique group of compounds of high stability and effective use. Thus, especially preferred embodiments comprise tin, chromium, or copper tetraethylaluminum or boron.

Further examples of the bimetallic organometallic plating agents, some of which are tailormade to produce the highly desirable lithium-aluminum alloys, include the following: lithium tetramethylboron, lithium tetraethylboron, lithium tetraethylaluminum, lithium triethylzinc, lithium tetraisopropylboron, lithium tetraoctylboron, lithium tetraoctylaluminum, lithium trioctylzinc, lithium tetraoctadecylboron, lithium tetraeicosylboron, lithium tetravinylboron, lithium tetra 2 butenylboron, lithium tetra-2- butenylalurninurn, lithium tri-Z-butenylzinc, lithium 1- hexynyl triethylboron, lithium tetraethynylboron, lithium tetracyclohexylboron, lithium tetracyclohexylaluminum, lithium tetraphenylboron, lithium tetrabenzylboron, lithium tetranaphthylboron, lithium tetracyclohexenylboron, lithium tetrabutadienylboron; lithium ethyltributylboron, lithium ethyldibutylcadmium, lithium ethyltrioctylboron, lithium ethyitrioctadecylboron, lithium ethyltricyclohexylboron, lithium ethyltriphenylboron, lithium ethy1tri 2- phenylethyl)boron, lithium ethyltriisopropylboron, lithium diethyldiisopropylboron, lithium diethyldiphenylboron, lithium diethyldioctadecylboron, lithium octyltrioctadecylboron; lithium ethylboron trichloride, trifluoride, tribromide, or .triiodide; lithium triethylboron hydride, lithium triethylaluminum hydride, lithium trioctylboron hydride; lithium ethyltrimethoxyboron, lithium triethylethoxyboron, lithium trioctylboron octanoate, lithium triethylboron or aluminum cyanide, lithium triphenylboron cyanide, lithium triethylboron cyanate and thiocyanate; lithium triethylboron amide, lithium triethylboron mercaptide, lithium triethylboron azide, lithium triethylboron acetate, lithium triethylboron octanoate, lithium triethylboron phenolate; lithium triethylboron, sulfate, nitrate, nitrite, sulfite, phosphate, phosphite, arsonate, or chlorate; potassium tetraethylboron, potassium tetraethylaluminum, lithium tetraethylboron, magnesium tetraethylaluminum, calcium tetraethylboron, magnesium tetraethylboron, strontium tetraethylboron, potassium ethyltriphenylboron, potassium triethylboron cyanide, potassium triethylboron chloride, potassium triethylboron cyanate, potassium triethylboron sulfate, and the like. It is to be understood that the hydrocarbon portions of the above and other bimetallic organometallic compounds can be further substituted with other functional groups which do not interfere with the reaction as, for example, the halogens, acid groups, both inorganic and organic, and the like. It is preferable that the R groups of the bimetallic organometallic be hydrocarbon groups, especially the lower alkyl in accordance with the present invention wherein at least one of the hydrocarbon groups is a cyclopentadienyl group arerlithiumboron tetrakis(cyclopentadienide), lithium aluminum 'tetrakis(cyclopentadienide), lithium aluminum tetrakis(methylcyclopentadienide), lithium gallium tetrakis (cyclopentadienide), lithuim indium tetrakis(ethylcyclopentadienide), lithium boron cyclopentadienide trihydride, lithium boron tris(cyclopentadienide) hydride, lithium aluminum tris(cyclopentadienide) hydride, lithium aluminumcyclopentadienide triethyl, lithium aluminum bis(cyclopentadienide) diethyl, lithium aluminum cyclopentadienide trimethyl, sodium aluminum cyclopentadienide triisobutyl, sodium aluminum cyclopentadienide diethylhydride, sodium aluminum cyclopentadienide trifluoride, sodium aluminum cyclopentadienide diethyl chloride, sodium aluminum cyclopentadienide ethyl dichloride, sodium aluminum cyclopentadienide ethyl dibromide, sodium aluminum cyclopentadienide ethyl difluoride, sodium aluminum cyclopentadienide ethyl diiodide, sodium aluminum tricyclopentadienide chloride, sodium aluminum tricyclopentadienide fluoride, sodium gallium *tricyclopentadienide ethyl, sodium gallium tetracyclopentadienide, sodium indium tetracyclopentadienide, sodium thallium cyclopentadienide trichloride, potassium boron tetracyclopentadienide, potassium boron tricyclepentadienide hydride, potassium boron tricyclopentadienide ethyl, potassium boron tricyclopentadienide chloride, potassium boron cyclopentadienide triethyl, potassium boron cyclopentadienide trihydride, potassium boron cyclopentadienide trichloride, potassium aluminum tetracyclopentadienide, potassium aluminum tetra indenide, rubidium aluminum tetracyclopentadienide, rubidium aluminum tetraethyl, cyclopentadienide, cesium boron tetraeyclopentadienide, cesium aluminum tetracyclopentadienide, beryllium bis(boron cyclopentadienide triethyl) beryllium bis(aluminum tetracyclopentadienide),berylliu bis (aluminum' tricyclopentadienide ethyl), beryllium bis (aluminum cyclopentadienide triethyl), magnesium bis boron tetracyclopentadienide), magnesium bis(boron tetraphenyl cyclopentadienide), magnesium bis(aluminum tetramethyl cyclopentadienide), magnesium bis(aluminum tricyclopentadienide chloride), magnesium bis (aluminum cyclopentadienide tribromide), calcium bis boron cyclopentadienide trichloride), calcium bis(boron cyclopentadienide trihydride), strontium bis(gallium tetracyclopentadienide), barium bis(indium tetrafluorenide), zinc bis'(boron tetracyclopentadienide), zinc bis(aluminum tetracyclopentadienide), zinc bis(aluminum cyclopentadienide triethyl), cadmium bis(alurniuum tetracyclopentadienide), mercury bis(boron cyclopentadienide trihydride), mercury bis(aluminum cyclopentadienide trihydride), mercury bis(aluminum cyclopentadienide trichloride), and mercury bis(gallium tetracyclopentadienide). In addition to the compounds above, similar compounds can be made containing other cyclopentadienyl groups including the isopropyl, diisopropyl, hexyl, tolyl, xylyl, and other alkyl and aryl derivatives of cyclopentadienyl groups.

When employing the bimetallic organometallic plating agents of this invention in the absence of a carrier gas, it is desirable to maintain enough vapor pressure below the decomposition temperature of the organometallic to enable the process to be conducted at an appreciable rate of plating. Too high vapor pressure results in poor substrate' adherence. Thus it is preferred to employ up to about mm. pressure during the plating operation; prefe'rably 0.01 to 10 mm. of pressure. When an inert carrier gas such as argon or other carrier gases such as hydrogen and carbon dioxide are employed in the process, it is desirable to employ a higher vapor pressure, e.g. between about 10 to 20 mm. of pressure. In this connection, however, it is to be noted that the partial pressure" of the bimetallic organometallic is about 0.01 to about 10 mm. pressure during the plating operation.

Although temperatures above the decomposition temperature of the organometallic plating agent are generally employed, (usually temperatures no higher than about 700 C. are used), a preferred temperature exists for each organom'etallic plating-agent. When'this temperature is employed betterplatingresultscan beobtained. At these temperatures exceptionally brighter, better adhering coatings are obtained.

By the term alloy as employed herein is meant a mixture of two or more metallic elements (or non-metals,

such as-Te, P) which have a metallic appearance and which are either: (1) A molecular mixture, microscopically homogeneous; (2) a colloidal mixture, microscopically heterogeneous; Hackhs Chemical Dictionary, 3rd edition (1944), McGraw-Hill Book Co., Inc., page 34.

In some cases more uniform'coating can be obtained through the employment of pack metallizing techniques. The plating agent when employed in such pack metallizing technique is a solid such as chromium tris(aluminum tetraethyl). One of the advantages of employing such pack metallizing techniques is that very uniform plating temperatures can be achieved because of the solid mate rials employed in this type of process. Pack metallizing involves packing the substrate to be plated into a metal or glass reaction vessel provided with a gas outlet means. (Usually a metal substrate is used.) With the plating agent is employed an'inert filler material such as sand, refractory powders or any other material inert under the application conditions. Thus the reaction vessel contains the object to be plated surrounded by the solid plating agent, the remaining space of the reaction vessel being filled with the aforesaid inert filler. The reaction container is thereafter placed in an induction heating furnace and the temperature of the furnace raised to a point above the decomposition temperature'of the plating agent. The following example'illustratesthis technique more fully.

Example X Compound Cr(AlEt '(chro'mium tris- (aluminum tetraethyl) Temp. of substrate 400 C. Nature of Substrate Mild steel. Pressure 0.1 mm. Time 1% hours. Results Dull, metallic. Method Pack metallizingi In addition to the thermal and ultrasonic techniques discussed hereinabove, other methods for decomposition of the bimetallic organometallic plating agents of the instant invention can also be employed. These other methods encompass other techniques such as decomposition of the bimetallic organometallic plating agent with ultraviolet irradiation. ln employing such a technique an apparatus substantially the same as employed in Example I is used with the exception that in place of the high frequency induction heating means a source of ultraviolet irradiation is employed. This ultraviolet technique is particularly applicable to those bimetallic organometallic compounds of this invention having good volatility characteristics.

Another decomposition technique which can be employed in achieving alloy plates from the plating agents of this invention involves chemical decomposition. Illustrative of such chemical decomposition is the decomposition of copper tetraethylaluminum by treating with acid (50 percent HCl) to produce a colloidal alloy deposition.

In general any substrate which is stable to decomposition at the temperatures employed in the plating process utilized are suitable substrates for this invention. Exemplary of the wide diversity of substrates which can be employed in the instant invention are metallic substrates such as ferrous metal substrates (particularly steel), aluminum, coper, yttrium, molybdenum, beryllium, and the like. Alloy substrates can also be employed which result in the deposition of an alloy upon an alloy material. Glass substrates such as Pyrex can be used. Other substrates which can be employed are ceramics, cermeis, refractories such as alumina, graphite and the like; plastics such as Teflon (e.g. polyfluoro hydrocarbons), and a multitude of cellulose materials such as Wood, cloth, paper, etc.

Other bimetallic organometallic plating agents can be employed in the above working examples to produce similar alloy plating on the substrate to be plated. Thus when tin tetramethylboron, scandium tetraethylboron, tin triethylzinc, titanium triethylzinc, potassium triethylboron chloride, sodium indium tetracyclopentadienide, beryllium bis(boron cyclopentadienide) triethyl, strontium bis(gallium tetracyclopentadienide), zinc bis(aluminum tetracyclopentadienide) are employed in the examples described above, alloy plates of the corresponding metals contained in each of these compounds are deposited upon the substrate plated.

The decomposition techniques of this invention can be varied so that, in some instances, substrates can be plated with one or both of the metals from the bimetalic organometallic compound while concurrently depositing therefrom metal powders. By such techniques it is possible to produce two useful materials from one plating agent, i.e. the plated article of manufacture and the concurrently deposited metallic powders.

The alloy depositions produced from bimetallic organometallic compounds according to the processes of this invention have many applications in the metallurgical and related arts. 'In the following working example the application of the processes of this invention to plating aircraft landing gear fabrication materials is illustrated.

Example X] A high performance steel aircraft landing gear structural member is placed in a conventional heating chamber provided with means for high frequency induction heating and gas inlet and outlet means. Lithium aluminum tetracyclopentadiem'de is placed in a standard vaporization chamber provided with heating means, said vaporization chamber being connected through an outlet port to the aforesaid combustion chamber inlet means. The member is heated to a temperature of approximately 350 C. and the system is evacuated. The lithium aluminum tetracyclopentadienide is heated to a temperature (about 150 C.) where it possesses vapor pressure of up to about mm. The lithium aluminum tetracyclopentadienide vapors are pulled through the system by a vacuum pump and they impinge on the heated aircraft landing gear structural member decomposing and forming a well adherent lithium-aluminum alloy coating over the entire surface of the structural member. In such a manner the structural member is coated with a high performance corrosion resistant lithium-aluminum alloy coating having high tensile strength for application to the extreme requirements of modern age aircraft.

We claim:

1. In a process for metal plating a substrate by decomposition of a metal containing compound in contact with said substrate, the improvement which comprises employing as said metal containing compound a bimetallic organometallic compound, containing at least two diiferent metals and wherein said organo group is an unsubstituted hydrocarbon group containing between about l-20 carbon atoms, and conducting said process in an inert atmosphere, essentially devoid of free hydrogen.

2. A process for plating a substrate comprising heating the object to be plated, in an inert atmosphere essentially devoid of free hydrogen, to a temperature above the decomposition temperature of a bimetallic organometallic compound and contacting said bimetallic compound with said heated object, said bimetallic organometallic compound being further defined as having the general formula wherein M is a metal selected from the groups consisting of groups I, H, III-B, IV-B, V-B, VI-B, VII-B, VIII, tin and aluminum; M is a difierent metal selected from the group consisting of group III-A, zinc and cadmium; R is a monovalent anion, x is an integer corresponding to the valence of the metal M, y is an integer corresponding to the valence M.

3. The process of claim 2 wherein said object is heated to a temperature above about 200 C. while maintained under an inert gas selected from the group consisting of nitrogen, neon, argon, krypton and xenon.

4. A process for plating a substrate which comprises heating said substrate to a temperature above the decom posit-ion temperature of tin bis(aluminum tetraethyl) and contacting the tin bis(aluminum tetraethyl) with said substrate; said process being conducted under vacuum; the (tin bis(aluminum tetraethyl) compound having a vapor pressure of up to about 10 millimeters of mercury.

5. A process for plating a ferrous metal substrate with an alloy of lithium and aluminum, which comprises heating said substrate to a temperature above the decomposition temperature of a bimetallic organometallic compound, wherein lithium, aluminum and an unsubstituted hydrocarbon group containing 1-20 carbon atoms are the exclusive constituents of the molecule, and contacting said compound with said substrate; said process being conducted under an inert atmosphere essentially devoid of free hydrogen.

6. A process for plating a substrate which comprises heating said substrate to a temperature above the decomposition temperature of lithium aluminum tetracyclopentadienide and contacting the lithium aluminum tetracyclopentadienide with said substrate; said process being conducted under vacuum; the lithium aluminum tetracyclopentadienide compound having a vapor pressure of up to about 10 millimeters of mercury.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS FOR METAL PLATING A SUBSTRATE BY DECOMPOSITION OF A METAL CONTAINING COMPOUND IN CONTACT WITH SAID SUBSTRATE, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS SAID METAL CONTAINING COMPOUND A BIMETALLIC ORGANOMETALLIC COMPOUND, CONTAINING AT LEAST TWO DIFFERENT METALS AND WHEREIN SAID ORGANO GROUP IS AN UNSUBSTITUTED HYDROCARBON GROUP CONTAINING BETWEEN ABOUT 1-20 CARBON ATOMS, AND CONDUCTING SAID PROCESS IN AN INERT ATMOSPHERE, ESSENTIALLY DEVOID OF FREE HYDROGEN. 